Effects and Molecular Regulation Mechanisms of Salinity Stress on the Health and Disease Resistance of Grass Carp

Abstract

Though some freshwater fish have been successfully cultivated in saline-alkali water, the survival rates of freshwater fish are greatly affected by different saline-alkali conditions. The mechanisms of immune adaptation or immunosuppression of freshwater fish under different saline-alkali stress remain unclear. Here, grass carp were exposed to 3‰ and 6‰ salinity for 30 days. It was observed that salinity treatments had no obvious effects on survival rates, but significantly increased the percent of unhealthy fish. Salinity treatments also increased the susceptibility of grass carp against Flavobacterium columnare infection. The fatality rate (16.67%) of grass carp treated with 6‰ salinity was much lower than that treated with 3‰ salinity (40%). In the absence of infection, higher numbers of immune-related DEGs and signaling pathways were enriched in 6‰ salinity-treated asymptomatic fish than in 3‰ salinity-treated asymptomatic fish. Furthermore different from salinity-treated symptomatic fish, more DEGs involved in the upstream sensors of NOD-like receptor signaling pathway, such as NLRs, were induced in the gills of 6‰ salinity-treated asymptomatic fish. However in the case of F. columnare infection, more immune-related signaling pathways were impaired by salinity treatments. Among them, only NOD-like receptor signaling pathway was significantly enriched at early (1 and/or 2 dpi) and late (7 dpi) time points of infection both for 3‰ salinity-treated and 6‰ salinity-treated fish. Besides the innate immune responses, the adaptive immune responses such as the production of Ig levels were impaired by salinity treatments in the grass carp infected with F. columnare. The present study also characterized two novel NLRs regulated by salinity stress could inhibit bacterial proliferation and improve the survival rate of infected cells. Collectively, the present study provides the insights into the possible mechanisms why the percent of unhealthy fish in the absence of infection and mortality of grass carp in the case of F. columnare infection were much lower in the 6‰ salinity-treated grass carp than in 3‰ salinity-treated grass carp, and also offers a number of potential markers for sensing both environmental salinity stress and pathogen.

Diverse Transcriptome Responses to Salinity Change in Atlantic Cod Subpopulations

“…NLRs play a crucial role in the inflammatory response by forming an inflammasome in the cytosol to protect the organism from pathogens and environmental factors [59]. The results of this study suggest that NLRs may act as sensors to salinity stress, which is in agreement with previous studies in grass carp (Ctenopharyngodon idella) [60]. In particular, the expression of CLRs and NLRs in the GDA and KIEL subpopulations depends on the transcript variant, which is in accordance with our previous study, and indicates that alternative splicing supports the response to the variable salinity environment in Atlantic cod [14].…”

Effects of Saline-Alkaline Stress on Metabolome, Biochemical Parameters, and Histopathology in the Kidney of Crucian Carp (Carassius auratus)

“…CA is considered a crucial stress factor as it affects the survival of aquatic animals in saline-alkali water [ 6 ]. Previous studies have shown that carbonate alkalinity could cause a series of problems for aquatic animals, such as respiratory and metabolic alkalosis [ 7 ], tissue oxidative damage [ 8 ], intestinal flora imbalance [ 9 ], as well as disorders of the antioxidant and immune system [ 10 ], which seriously affect the normal growth, development and reproduction of fish. At the same time, recent studies have shown that the extent of freshwater salinization continues to deepen as a result of human activities and global warming, which might steadily shrink the available space for freshwater aquaculture [ 11 , 12 ].…”

The Effect of Salinity Stress on Enzyme Activities, Histology, and Transcriptome of Silver Carp (Hypophthalmichthys molitrix)

“…Because inland waters are more polluted and cyanobacteria blooms frequently occur, silver carp are often exiled into lakes and reservoirs, where they proliferate extensively, to control the abnormal growth of algae and obtain economic benefits [ 22 , 23 ]. Currently, many studies have been conducted on the effects of salinity on freshwater fish [ 24 , 25 , 26 ]. Some freshwater fish have been successfully cultivated in saline–alkali water, including crucian carp ( Carassius auratus gibelio ), grass carp ( Ctenopharyngodon idella ), bighead carp ( Hypophthalmichthys nobilis ), medaka ( Oryzias latipes ), and channel catfish ( Ictalurus punctatus ) [ 26 ].…”

“…Currently, many studies have been conducted on the effects of salinity on freshwater fish [ 24 , 25 , 26 ]. Some freshwater fish have been successfully cultivated in saline–alkali water, including crucian carp ( Carassius auratus gibelio ), grass carp ( Ctenopharyngodon idella ), bighead carp ( Hypophthalmichthys nobilis ), medaka ( Oryzias latipes ), and channel catfish ( Ictalurus punctatus ) [ 26 ]. This not only results in the improved utilization rate of saline–alkali water but is also important economically for the aquaculture of freshwater fish in saline–alkali areas.…”